Water quality standards

Water quality standards:

  • Protect water resources for uses such as fishing, swimming and other recreation, and sustaining fish, bugs, plants, and other aquatic life
  • Are a measure to identify polluted waters or healthy waters in need of protection
  • Guide the limits set on what regulated facilities can discharge to surface water

The federal Clean Water Act requires states to designate beneficial uses for all waters and develop water quality standards to protect each use. Water quality standards consist of several parts:

  • Beneficial uses — Identify how people, aquatic communities, and wildlife use our waters
  • Numeric standards — Amounts of specific pollutants allowed in a body of water and still protects it for the beneficial uses
  • Narrative standards — Statements of unacceptable conditions in and on the water
  • Antidegradation protections — Extra protection for high-quality or unique waters and existing uses

Together, the beneficial uses, numeric and narrative standards, and antidegradation protections provide the framework for achieving Clean Water Act goals. The Clean Water Act specifies healthy aquatic life and recreation as beneficial uses. Others that are protected in Minnesota's rules are:

  • Drinking water
  • Industrial and agricultural uses
  • Wildlife
  • Navigation
  • Aesthetic enjoyment

Minnesota’s water quality standards are provided in Minnesota Rules chapters 7050 (Waters of the State), and 7052 (Lake Superior Basin Water Standards). Details of how water quality standards are implemented in point-source discharge permitting are contained in Minnesota Rules chapter 7053 (State Waters Discharge Restrictions), and parts of chapter 7052.

All current state water rules administered by the MPCA are available on the Minnesota water rules page.

Current water standard projects and priorities

The MPCA is continually working to revise, develop, or otherwise improve Minnesota’s water quality standards. The process for developing and codifying water quality standards can take months and often takes years. The agency must establish the technical basis and create supporting documents for the standard, ensure peer review, and give the public the opportunity to comment on their proposal. The U.S. Environmental Protection Agency has final authority to approve or disapprove any new or revised standards.

PDF icon Inventory of water quality standards projects, 2021-2023 (wq-s6-35)

Overview and status of water quality standards projects the MPCA has prioritized for 2021 to 2023. The inventory reflects the priorities identified in 2020-2021 triennial. The inventory is updated every year by December 15.

See the 2021-2023 work plan for more information about the expected development of these water quality standards.

The rulemaking docket has more information about the status of water quality standards projects in rulemaking (Group 1 in the inventory): PDF icon Public Rulemaking Docket (mm-rule1-00)

Elements of standards

Water quality standards are the fundamental regulatory and policy foundation to preserve and restore the quality of all waters of the state. They consist of three elements:

  • Classifying waters with designated beneficial uses;
  • Narrative and numeric standards to protect those uses; and
  • Antidegradation policies to maintain existing uses, protect high quality waters, and preserve waters of outstanding value.

Beneficial uses

Seven use classes are outlined in Minnesota’s water quality standards rules.

  • Class 1: Domestic consumption
  • Class 2: Aquatic life and recreation
  • Class 3: Industrial consumption
  • Class 4: Agricultural and wildlife
  • Class 5: Aesthetics and navigation
  • Class 6: Other uses
  • Class 7: Limited Resource Value Water (LRVW)

These use classes reflect the multiple beneficial uses that Minnesota’s surface waters provide, and accordingly all surface waters are assigned multiple use classes.  All groundwater is assigned the Class 1 beneficial use of domestic consumption (drinking water).

Surface waters that cannot meet Class 2 aquatic life and recreational uses are Class 7 waters, otherwise known as limited resource value waters. Class 7 waters are still expected to meet standards that are protective for downstream waters and other beneficial uses.


Numeric standards are allowable concentrations of specific chemicals that, when present in a water body, will protect designated beneficial uses.  They also include measures of biological health.  Numeric standards are derived using methods provided in Minnesota rules and are specific to each beneficial use.  This means a numeric standard that protects Class 2 waters for aquatic life and recreation may be different from a numeric standard for the same pollutant that protects Class 4 waters for agricultural uses and wildlife. When numeric standards exist for more than one beneficial use class, the most stringent value applies.

If the numeric standard is not exceeded, the water body meets the use class goal.

Some standards are narrative rather than numeric. A narrative water quality standard is a statement that prohibits unacceptable conditions in or upon a water body. Narrative standards address very fundamental and basic forms of water pollution, such as floating solids, scums, visible oil film, or nuisance algae blooms. Some narrative standards are more involved and set water quality goals in connection with specific pollutants or concerns, such as eutrophication, and pollutants that accumulate in fish and are harmful to fish consumers (people and wildlife).

The MPCA conducts biological monitoring and employs the recently adopted Tiered Aquatic Life Uses (TALU) framework to provide a more direct method to assess biological health; biological monitoring complements the information provided by chemical (pollutant) monitoring. Both data sets are used to assess whether Class 2 aquatic life uses are being met.

Numeric and narrative standards are not available for all pollutants and water quality concerns. When needed, Minnesota rules provide for the development of site-specific criteria to address pollutants and concerns for which standards are not available. Also, numeric standards in rule can be modified based on site-specific data. More information about both is available on the site-specific water quality standards webpage.


Antidegradation (formerly referred to as nondegradation) is the third element of water quality standards.  Antidegradation protections help maintain high quality waters (waters better than what is necessary to protect aquatic life and recreation) from deterioration. Antidegradation protections were established to provide future generations with the opportunity to enjoy high quality and highly valued recreational and aesthetic resources that might suffer degradation without them. Preventing degradation is almost always less costly and more effective than restoration, which cannot always be fully achieved.

Three levels of protection are incorporated into antidegradation rules:

  1. Existing uses of the water body must be maintained and protected.
  2. Existing high water quality must be maintained unless a lowering of water quality is deemed necessary to accommodate important economic and social development.
  3. The exceptional characteristics of specific waters designated in Minnesota rules as outstanding, very sensitive, or unique resources — outstanding resource value waters or ORVWs (Minn. R. 7050.0335) — must be maintained and protected. Minnesota rules specify two classes of ORVWs: "prohibited" and "restricted":
  • ORVWs listed as prohibited include waters within the Boundary Waters Canoe Area Wilderness and Voyageurs National Park. New or expanded discharges are banned in these and other prohibited ORVWs.
  • ORVWs listed as restricted include portions of Lake Superior, and federal and state designated scenic and recreational river segments such as the St. Croix River. New or expanded discharges are controlled in restricted ORVWs to maintain their exceptional character.

Additionally, all surface waters in the Lake Superior basin are designated as outstanding international resource waters (OIRWs). Antidegradation protections for the Lake Superior basin focus on reducing the contribution of bio-accumulative pollutants to the basin.

How to determine the beneficial uses of a particular waterbody

Generally speaking, all of Minnesota’s surface waters are protected for Class 2 aquatic life and recreation uses unless the waterbody has been individually assessed and re-classified as a Class 7 limited resource value water.  In addition, because Minnesota’s water quality standards incorporate multiple beneficial uses, all of Minnesota’s surface waters are also protected for at least one subclass within Use Classes 3, 4, 5 and 6.  

Determining the specific uses and subclasses for which an individual waterbody is protected requires a little research. Waterbodies whose classification is provided in Minnesota rules are termed “listed waters.” All other waters receive default classifications and are termed “unlisted waters.”

Listed waters. Minn. R. 7050.0470 identifies “listed” waters and their associated use classifications. The listings in Minn. R. 7050.0470 are arranged by the nine major Minnesota watersheds with streams provided first, followed by lakes and wetlands.

Note that for streams, the beneficial use classifications are no longer in the rule itself; they are incorporated by reference. Lakes and wetlands are listed directly in Minn. R. 7050.0470.  

Minnesota R. 7050.0410 and 7050.0420 provide the additional uses for which all listed waters are protected.

The vast majority of surface waters are not listed and will not be in Minn. R. 7050.0470.

Unlisted waters. If the waterbody of interest is not found in Minn. R. 7050.0470, then Minn. R. 7050.0430 applies. This section of rule classifies all unlisted waters and provides the specific beneficial uses that apply.

Occasionally waterbodies may be referred to by more than one name. If in doubt about the classification of a waterbody of interest we suggest you consult MPCA staff listed in the Contacts tab.

Draft Technical Support documents

A key part of proposing new or revised WQSs is developing the technical foundation behind the narrative and numeric WQSs. MPCA develops this foundation based on review of scientific data, consideration of relevant rules, guidance, public comments, and consultation with topic experts at the U.S. Environmental Protection Agency (administrator of the CWA), other state agencies, Tribal Authorities, and academic researchers. The product of this review are topic-specific Technical Support Documents (TSDs) that will later be introduced in the rulemaking record as the supporting documents (exhibits) to the proposed rules and Statement of Need and Reasonableness (SONAR). The goal of publishing these documents prior to the official notice for proposing revised rules and SONAR is to obtain early comments and additional data to help MPCA refine and improve the basis for the proposed water quality standards.

TSDs are available on the following topics (note: not all topics being revised as part of the scope of this review have TSDs available):

Supporting Information for WQS

When MPCA adopts revised WQS into rule (Minnesota Rules Chapters 7050 and 7052) there are extensive technical and other documents cited as exhibits or included in the Statement of Need and Reasonableness (SONAR). The supporting information is available from the MPCA File Managers upon request. For recent rulemakings, this webpage provides important reference documents and citations for WQS users to find primary supporting information on the following WQS:

Eutrophication standards for lakes/reservoirs and rivers

Final rule notices published in State Register, March 10, 2008, volume 32, pp. 1699-1728 and August 4, 2014, volume 39, pp. 154-6.

PDF icon Review of river eutrophication standards for the Minnesota River: Summary of findings (wq-s6-62) (April 2020)

PDF icon Minnesota Lake Water Quality Assessment Report: Developing Nutrient Criteria, Third Edition (wq-lar3-01) (September 2005)

HTML icon Minnesota’s approach to lake nutrient criteria development (2008)

PDF icon Minnesota Nutrient Criteria Development for Rivers (wq-s6-08) (January 2013)

PDF icon Mississippi River Pools 1 through 8 - Developing River, Pool and Lake Pepin Eutrophication Criteria (wq-s6-09) (September 2012)

PDF icon Lake Pepin Site Specific Eutrophication Criteria (wq-s6-10) (March 2011)

HTML icon Development of eutrophication criteria for Minnesota streams and river using multiple lines of evidence (June 2015)

PDF icon Regionalization of Minnesota’s rivers for application of river nutrient criteria (2019) (wq-s6-18)

Total suspended solids (TSS)

Final rule notice published in State Register: August 4, 2014 (vol. 39, pp. 154-6)

PDF icon Aquatic Life Water Quality Standards Draft Technical Support Document for Total Suspended Solids (Turbidity) (wq-s6-11) (May 2011)

Human health methods revision for Class 2 chronic standards and criteria

Final rule notice published in State Register, March 16, 2015, volume 39, pp. 1344-46

PDF icon Human Health-based Water Quality Standards technical support document (wq-s6-12a) (June 2017)

MPCA contacts on water quality standards and rulemaking

Anti-degradation and unit supervisor

Economic analyses

Human health and aquatic life standards and site-specific criteria

Impaired waters list

PFAS (per- and polyfluoroalkyl substances)

Site-specific modified standards

Tiered aquatic life uses

Triennial standards review coordinator

Use classifications


More information on water quality standards